SN2001 Overheats with T stat but runs cool without

Hello fellow correct crafters- I have a 1988 SN 2001. I'm celebrating 15 years with this boat. However this season I have been chasing an overheating issue all summer long. Short Story - day 1 overheated, day 2 replaced impeller with a used one. Day 3 - ran cool. Day 4 Installed new impeller, day 5 overheated. Day 6 - removed t stat and boat ran cool 140-160 degree. Day 7 - Replaced T-stat with 160 from ski dim and back to overheating. Day 7, part 2 - took new t-stat out and ran the whole lake yesterday - 5 miles up and 5 miles back, boat tended to stay cool for the most part, looked like it had a hard time settling in at a consistent temp. But for the most part ran about 1`60. SO here is my question: why does it overheat with the t stat in, even a new t-stat? Why does it run cool without and what problems do I have to look forward to should I run it with a t stat regularly. Thanks CCF! See you on the lake

160 with no t-stat seems kinda high.   If you don't have a raw water strainer, have you checked the inlet end of the transmission cooler for debris?

Agree with cbrdude. Get an IR temp gun and check the temp around the sending unit. Make sure it's really overheating and not just a bad dash ground.

Oh, wow thanks for all the replies. My problem fell on deaf ears over at Planet Nautique. For the record my first impeller came out shredded so there is a good likelihood of having to chase down and remove chunks of impellers.

8122pbrainard - agreed the new T stat could be bad. Maybe Its worth $40 to try another one.
MACS81SN - agreed that 160 was high but I didn't hear that these boats came with 143 degree when new until after I bought it. Also my boat has run at 160 since I owned it so I thought that was thew right one. Maybe I should get a 143 degree and see if that helps.

Do you know of the least inexpensive place to buy one? I guess SKIDIM and another $40 should do it??

As far as the raw water strainer, I do have the plastic "jar" with the screen an O ring. Is that what you are referring to? I just replaced with new the jar and the o ring and the screen looked fine., Its full of what while the boat is running.
Trans Cooler - this is something I'd like to check out, what is the process to determine if there is a clog going over to the trans? Not sure exactly where to start or what I'm looking at?

cbr1000dude - not sure if a temp gun makes sense because with T-stat - temp spikes quickly. With out stat temp comes down to 160 range. So it seems to be sending the consistent message to the gauge. Since the 15 years I've owned the boat I did replace complete exhaust including new exhaust manifolds. about 5 years ago. Could the be blocked? Yes I guess so, it should be easy enough for me to remove. Once removed can I blow them out with a hose? How does one go about removing and obstruction?

bb12 - I hear you but like I said T-stat removed, engine runs cool, T-stat installed (old or new 160 from skidim) boat overheats.

8122pbrainard and bb12 - to satisfy this requirement, at some point beofre I bring my boat to a third party which is going to cost a S*&t ton of money where I live, I'll replace both the sending unit and the gauge to rule this out. I am pretty familiar with all the gauges and all the wires behind my dash to the extent that that all my gauges appear to be working correctly. Unless there is some correlation between installing a t-stat and somehow knocking the gauge/sending unit function out. However, I'd like to so this as second or third attempt.

My first attempt will be somehow clearing out blocked passages, as my current situation doesn't appear to "flow" once T-stat get dropped in. Any help on where to start/take apart/look would be appreciated. Also if any process like blowing out with a garden hose can be explained to me - I'd like to try that too.

Second attempt I'd like to try and get a 143 degree t-stat - any economical link to the correct product would be appreciated. Thanks again CCF Community.

UndercoverPoe wrote: Day 1 overheated Day 2 replaced impeller with a used one. Day 3 - ran cool. Day 4 Installed new impeller Day 5 overheated. Day 6 - removed t stat and boat ran cool 140-160 degree. Day 7 - Replaced T-stat with 160 from ski dim and back to overheating. Day 7, part 2 - took new t-stat out and ran the whole lake yesterday - 5 miles up and 5 miles back, boat tended to stay cool for the most part,

What caused the initial overheat? When exactly did you replace the strainer jar?

Have you tried going back to your used impeller (with thermostat)? Where did you get the new Day 4 impeller?

You're screwing around with the thermostat and that's clearly not the issue. Use a genuine Sherwood or PCM impeller.

Quote : with T-stat - temp spikes quickly. With out stat temp comes down to 160 range.

T- stat in backwards???

On all my CCs I have installed a faucet after the trans cooler so I can have a positive water flow for running on dry land. Those "fake a lake" devises can fall off when getting in and out of the boat in my experience. So blowing water backwards through the trans cooler happens every time I hook up the garden hose. You can just disconnect the TC hose to the strainer and flush it there.
Also I run my Barefoot 454 without a thermostat on purpose. A huge engine under a cover doesn't need any help getting hot on a 100 degree day to me. I'm much more concerned about overheating than getting the oil hot enough, I change it often anyway.
Yes those pieces of impeller can get lodged anywhere and cause a problem.
Walmart has a IR temp gun for $11.99, so not checking actual temp in various spots seems like penny wise and pound foolish even though you have new risers. Yours aren't as corroded as mine, but raw water cooling means anything, silt for example, can collect in fittings. You might be able to clear it with a long screwdriver or flexible picker upper tool.depending on the angle.

Tstat can be checked in pan of water on stove. Just wipe off the meat thermometer before putting it back in drawer. Who knows, might add flavor!

WOW! Thanks for quick replies. T stat in backwards. Hmmmm. I never thought of that. I put it in pointy side up. As mentioned above, Is that the correct orientation?

My boat seems to go through T stats all the time. I was interested in your thread but in my case like mentioned above the temp barely gets above 120 with it out. The very first thing you said about your impeller being shredded would be my best guess. I bet you have a piece blocking somewhere.

How do you winterize? We used to do the suck and displace method. The first time I pulled the drain plug I was shocked by the amount of scale especially from the exhaust manifolds.

Clogged up riser passages are known to cause engines to run hot.

throttle out wrote: [QUOTE=*mtrbtr*] Also, be sure to tighten ALL of your hose clamps with a nut runner or socket and get them goodntight, do not use a screw driver.

Except take it easy on transmission oil cooler, as you can crush the shell.

The orientation of the impeller doesn't matter. It will "comb" the vanes the right way once it gets going. On the other hand though, I wouldn't re-install an impeller, where the vanes have taken a set, the other way. Of course, if the vanes have taken a set, the impeller is probably tired anyway.

I have heard of cheap impellers just not pumping, or the hub of the impeller breaking free and not spinning the impeller when the engine is running.

As far as cleaning out, you just have to follow the whole chain of the cooling system.
-Unlikely, but make sure there is nothing (like a plastic bag) jammed in the hull pickup
-Follow the hose and make sure your water strainer isn't clogged or cracked and that the rubber o-ring seal is in place
-check the transmission cooler doesn't have any debris clogged in the input side
-make sure none of the hoses are kinked or collapsing
-check the thermostat housing for impeller fragments or other clogs
-check the manifold fittings for debris
-along the way make sure all the hose ends are properly seated onto their fittings and that the hose clamps are snug but not too tight on the transmission cooler

Gary S wrote: And remove the pump and change impeller and gaskets on the work bench. Doing handstands trying to seat the impeller and align O rings and gaskets is,IMHO,looking for trouble too. Note that external screw for impeller cam should be facing out away from engine when pump is mounted back on engine.

Note to self: read this before replacing impeller.